German Patent No. DE 101 00 767 A1 describes a charging device in which, during operation in an allocated readiness mode, i.e. in standby operation, the power element is separated from an input-side voltage supply network by opening a mechanical switch. When an electrically conductive connection is created between the charging device and a battery pack that is to be charged, a current or voltage detector allocated to the charging device detects the battery pack and, using its residual voltage, activates the control unit in order to bring about a closing of the mechanical switch and thus a transition of the charging device to an allocated charge operating mode in order to charge the battery pack.
A disadvantage of previous devices is that the detection of highly discharged battery packs is particularly critical and can be liable to error. In addition, an existing residual voltage of the battery pack may not be adequate for the activation of the control unit, so that a secure and reliable charging of the battery pack cannot be ensured in all cases.